In recent year, with the development of urbanization process of each country, and utilization of underground space become an important trend in this field. Underground structures are used more and more widely in urban constructions, transportation, national defense constructions, and water conservancy projects such as railway tunnel, subway engineering, underground markets and air defense works. It has been showed that 21st century is the century of development and utilization of underground spaces. Moreover, the development of underground space and construction of the underground structure are in peak hours with fast development all over the world. As for urban traffic, subway engineering as an efficient public transport with large volume plays an important role in solving the problem of transportation. Though development of underground works is booming, it also faces challenges such as an earthquake. Especially in M7.2 Kobe earthquake in Japan 1995, the underground structures were damaged the most in history, and subway, underground parking, underground tunnel, and the underground market are damaged severely. The most remarkable thing is the damage to subway stations, and there is 5 subway station, and 3 km tunnel of the subway are damaged. The most damaged subway station is Daikai station, more than a half of central columns are completely collapsed, and this leads to the slump of top slab and the subsidence of overlying soil. The maximum settlement was 2.5 m. Research shows vertical earthquake may be the important factors to lead underground structures damaged, especially for shallow underground structures in which shear failures may occur in overlying soil at the beginning of an earthquake. At this moment, there is not a continuous entire structure with other soil surrounded the underground structure. In later seismic responses, the top slab of the underground structures may be surrounded, and weak connection heaped soil effect may occur, which is similar to the backfill. Restraint of underground structure and responses to the earthquake are different from the continuous soil. Vertical force evaluation of key support components of underground structures is influenced strongly by vertical inertia force of overlying soil. In fact, the force changes the axial compression ratio of the column, and shear resistance strength and deformation performance of the column are changed. As for the seismic response of the underground structure, increasing of shear resistance strength and decreasing of ultimate deformation performance of central column are disadvantageous. This means that the column will bear larger horizontal shearing force from underground structures caused by soil deformation, while decreasing of ultimate deformation performance may cause column damaged before side walls are broken, resulting in overall damages to the top slab and underground structures.
The present disclosure discloses an n-shape connected split column for underground structures based on seismic hazard features and failure mechanisms of the underground structures; it is used for replacing ordinary cast-in-place reinforced concrete column in traditional underground structure. The prefabricated reinforced concrete column is fully packaged by exterior sheet steel after connecting with the n-shape connector, connection gap between prefabricated reinforced concrete columns is not exposed to ensure the safety of split column; and shear failure of the overlying soil of underground structure is easy to occur under seismic action. Underground structures will bear larger longitudinal impedance load under the action of self-weight and additional vertical inertia force. The split column mentioned above is used to replace an ordinary cast-in-place reinforced concrete column in traditional underground structure to overcome the deficiency of horizontal deformation under high axial compression of ordinary reinforced concrete column in traditional underground structure, while relative deformation between prefabricated reinforced concrete columns drives the shear deformation of n-shape connector and dissipates some of the seismic energy such that key support components of underground structure are prevented from being damaged.